The present invention relates to a new and improved method of folding multi-sheet paper products, especially for applying a further longitudinal fold to paper products in the form of newspapers having a transverse break, and further, the invention pertains to novel apparatus for the performance of the aforementioned method.
During the folding of multi-sheet paper products phenomena arise with increasing thickness of such products, which at least are disturbing, when the paper product is again opened. These phenomena are attributed to the fact that theoretically it is only the innermost situated sheet of the fold which is to be formed which in the strictest sense really is "folded," whereas the remaining sheets so-to-speak are more or less "bent" about the "fold" of each next inner sheet. Therefore, during the folding operation the sheets of the paper products, which are comparable to the layers or plies of a layered product, must be capable of displacement relative to one another. Yet, particularly when forming the folds by automatic folding machines, this possibility of achieving such displacement is not always ensured, particulary in those cases where there is already formed in the paper product a pre-fold extending transversely with respect to the fold to be formed. If, however, during the course of the folding operation there is not possible such displacement of the sheets relative to one another, then the spine of the fold tends to so-to-speak "split," i.e., the outermost sheet or sheets of the fold tear or, however, there occurs an undesired creasing of the innermost sheets. To understand this more fully, reference at this point will be made to FIGS. 1, 2a, 3a, where the foregoing shall be explained in detail in conjunction with the folding of a newspaper.
Now in FIG. 1 there is shown a newspaper 10 composed of a number of sheets 11 which have been thrice commonly folded. The first performed fold, referred to in the art as the "first longitudinal fold," has been designated in the drawing by reference character 12 and the next subsequent fold which is formed, designated in the art as the "transverse break," is designated by reference character 13. If the newspaper is again folded and, specifically, transverse to the transverse break 13, then there is formed a second longitudinal fold, or, as it is referred to the so-called "post office fold" or briefly "post fold" 14. This expression "post office fold" is predicated on the fact that certain postal authorities refuse to handle single copies if they are in a shape of format resulting from the transverse break 13. FIGS. 1 and 3a illustrate the newspaper in a position where it is halfways open about such post fold 14. When producing the post fold or post office fold 14 there is not possible a relative displacement of the sheets 11 with respect to one another owing to the presence of the transverse break 13 and also the first longitudinal fold 12. As a result the sheets located innermost at the post fold 14 are creased. This can be clearly recognized by referring to FIG. 2a where there is shown a photographic section through the newspaper 10 with closed post fold 14 at the region of the transverse break 13. Now if the newspaper of FIG. 2a is opened then such creases appear in the form of ray-like crease folds 15 which emanate from the intersection point of the post fold 14 with the transverse break 13. These crease folds 15 are disturbing and can retard the readability of the printed text appearing at the innermost sheets near the post fold 14. This becomes even more disturbing since at the sheet innermost with respect to the post fold 14 there also is printed the title sheet or the final sheet of the newspaper, and these, as is well known, have particular significance in promoting the sale of the newspaper and attracting the attention of a potential reader.
Now in order to avoid these crease folds, German Pat. No. 931,656 has already proposed perforating the sheets at the location of the second longitudinal fold and then, after producing the transverse break, but prior to producing the second longitudinal fold, separating these sheets along the perforations. However, when doing so there appears at the centre of each sheet a slot, which is just as, if not more, disturbing than the aforementioned crease folds.